Project Description This application proposes to continue study the immune factors that are important for the pathogenesis of Th17 autoreactive T cells. We have made significant progress in investigating the mechanisms by which pathogenic Th17 (IL-17+) and Th1 (IFN-?+) autoreactive T cells cause autoimmune disease, and in studying whether the regulation of the pathogenic Th17 response differs from that of the Th1 response in the previous funding period. Our studies demonstrated that enhanced ?? T cell activation is a critical pathologic step response that leads to Th17 responses, raising the question whether manipulation of ?? T cell activation can prevent undesired Th17 responses. Based on our new findings that i) regulatory effect of ?? T cells is closely associated with adenosine; ii) activation of adenosine receptors (ARs) is an important factor of ?? activation, leading to augmented pathogenic Th17 responses; and iii) reciprocal interactions between ?? T cells and adenosine-mediated regulation determine the pathogenic Th1 and Th17 responses, we propose to continue determine the differences in regulatory mechanisms between Th1 and Th17 responses (Aim1) and determine the mechanism by which adenosine differently regulates Th1 and Th17 autoimmune responses (Aim 2). The hypothesis of this application is that the dendritic cells are critically involved in ??-mediated and adenosine- mediated regulation. ?? T cells are able to enhance DCs? ability of promoting Th17 responses and promote the generation of DC subset(s) that have greater ability of promoting Th17 responses. We will also determine the mechanism(s) by which adenosine inhibits Th1 responses but enhances Th17 responses. The proposed studies will exploit available knockout mice lacking A2ARs or CD73 and determine whether the proinflammatory effect of ?? T cells on the Th17 response is limited if their ability to bind adenosine is reduced, whether selective A2AR agonists/antagonists can effectively manipulate Th17 responses, whether manipulation of the enzymatic function of CD73 is effective in controlling the Th17 response, and whether adenosine degradation enzyme (ADA) and ADA inhibitors are effective in manipulation of the regulatory activity of ?? T cells and thus Th17 response. Successful accomplishment of the proposed studies should elucidate the molecular and cellular mechanism by which adenosine regulated autoimmune Th1 and Th17 responses and further clarify the pathogenic role of, and relationship between, IFN-?+ and IL-17+ autoreactive T cells in EAU should contribute to our understanding of the mechanism of autoimmune disease pathogenesis.